Blood pressure is a vital physiological measurement often used to assess the health and condition of an individual. A patient may be prescribed special medication or encouraged to take up an exercise regimen if blood pressure readings are higher than normal values defined based on the patient's age, weight, sex, or other characteristics. In addition, blood pressure readings may also be used to identify patients at risk of kidney failure, stroke, heart attack, or other serious, potentially life-threatening medical risks. Accordingly, blood pressure is a vital measurement and accurate blood pressure readings are critical to assessing a patient's health.
The standard method of obtaining blood pressure measurements uses pressure typically applied at a patient's bicep to determine the patient's diastolic and systolic blood pressure. A sphygmomanometer, which includes an inflatable cuff with a manometer to read pressure, is placed around a patient's arm and the inflatable cuff is inflated to apply a pressure to the patient's arm that is sufficient to occlude the patient's blood vessels. A medical practitioner uses a stethoscope to listen for the patient's pulse at a location on the arm distal from the cuff. When the vessels are occluded, no pulse is present and the practitioner hears no sounds. A release valve in the cuff is then opened, gradually releasing air from the cuff and decreasing the applied pressure. When the pressure in the cuff falls below the patient's systolic blood pressure, circulation in the arm begins as the vessels are no longer occluded. The circulation causes an audible heartbeat sounds, commonly referred to as Korotkoff sounds, that are detectable by the medical practitioner. The pressure in the cuff at the time these sounds begin is marked as the systolic pressure. The air in the cuff is then released until the pulse sounds are no longer audible, and the pressure in the cuff at which the pulse sounds disappear is recorded as the patient's diastolic blood pressure.
When a patient's blood pressure is measured, the pressure suddenly applied to the arm alerts the patient that a reading is being taken. Especially for patients who regularly experience a level of anxiety during clinical visits, this may trigger an involuntary increase in the patient's heart rate or tensing of the patient's muscles. The elevated stress level of the patient may cause inaccurate blood pressure measurements that are artificially increased by the patient's anxiety. This phenomenon is commonly referred to as the white coat effect, and can lead to improper diagnoses of hypertension. The increased pressure applied to the patient's arm, which is necessary for traditional blood pressure measurement, may thus serve as a stimulus for artificial increased blood pressure and inaccurate measurements.
Standard blood pressure measurements also create problems in obtaining consecutive blood pressure readings from a patient. When the inflatable cuff is inflated to occlude the blood vessels, the vessels and the patient's tissue are place under a high degree of compression. Due to inelastic properties of the vessels and tissue, this compression is not immediately relieved when the cuff is removed from the patient. Thus, a subsequent blood pressure reading taking immediately after a first reading is not reliable, as errors are introduced by the partial compression of the patient's tissue. A second reading can be accurately obtained from the patient's second arm, but this is inconvenient and still creates problems for readings beyond the second measurement.